The invention relates generally to the art of integrated circuit processing, and in particular to etching integrated circuit substrates.
Integrated circuits, such as semiconductor devices, are conventionally fabricated using a variety of well known processing techniques including sputtering, plasma etching, reactive ion etching, and the like. During the integrated circuit fabrication process, a variety of layers of insulating materials, passivating materials and metals are deposited on a substrate. The layers are patterned to provide the desired electrical circuits, conductors, and the like by selectively removing portions of one or more of the layers. Plasma processing, including sputtering, etching and ashing is a well-established and accepted technology employed in the fabrication of integrated circuits. A plasma etch process typically involves a plasma of gases applied to the substrate in a plasma chamber. Masking materials may be applied to portions of the substrate to protect such portions from the plasma gases while portions exposed to the plasma gases are etched. In other words, the plasma gases may be selected to preferentially etch one or more of the exposed layers over others of the exposed layers.
During the plasma processing step, atomic and molecular species are present in the plasma chamber. These species are derived from the plasma gases and the decomposition products from the etching process. The gaseous atomic and molecular species present in the plasma chamber produce radiative emissions that are characteristic of the particular species present in the chamber. Spectral analysis of the emissions may be used to identify the atomic and molecular species present in the plasma chamber, thereby indicating the progress of the etching process. A plot of optical emission intensity may be used to detect the end point of an etching step. Accordingly, the end point of an etching step may be indicated by a sudden increase or decrease in a particular spectral emission or a sudden change in slope of the emission intensity over time. These events tend to relate to a point in time when the last traces of a layer being etched are removed and the underlying layer is exposed to the etching plasma. End point detection thus tends to be an important control parameter for successful plasma etching.
One problem associated with the use of spectral emissions is that the intensity of the emissions is affected by a variety of factors including an increase over time of decomposition products and other materials on the chamber window through which the spectral emissions are monitored. Then another change occurs when the chamber window is cleaned of the deposits. Furthermore, the sensitivity of the different photo detectors used for different plasma chambers may vary from unit to unit and from chamber to chamber. Also, the absolute intensity of the emissions detected by photo detectors for multiple plasma chambers and used by a host computer may not be stable or may be difficult to match from chamber to chamber. Accordingly, there is a need for improved methods and apparatus for processing integrated circuits.
The above and other needs are met by a method for detecting an end point of an etching step conducted in an etching chamber. A target emission intensity level is selected for the etching step, and the etching step is performed in the etching chamber. A raw emission intensity level is sensed from the etching chamber during the etching step with an emission intensity level detector. The raw emission intensity level sensed from the etching chamber by the emission detector is modified with an emission intensity level modifier. The raw emission intensity level sensed with the emission intensity level detector from the etching chamber during the etching step is adjusted to the target emission intensity level by adjusting the emission intensity level modifier. The etching process is stopped upon occurrence of a predetermined spectral event sensed by the emission intensity level detector.
By using the emission intensity level modifier to set the sensed raw emission intensity level to a target emission intensity level at the beginning of each etching process, a baseline is created whereby the differences between emission intensity level sensors, cleanliness of an etching chamber over time, and variations between different etching chambers can be substantially removed from consideration in determining the end point of the etching process conducted in the various etching chambers.
In a preferred embodiment, the step of selecting a target emission intensity level for the etching step is accomplished by sensing a raw emission intensity level for a plurality of etching chambers. The lowest raw emission intensity level sensed from the plurality of etching chambers is determined and multiplied by an intensity factor to produce a result. The result is selected as the target emission intensity level for the etching step in each of the plurality of etching chambers.
In the most preferred embodiments, the intensity factor is less than one, and the step of sensing a raw emission intensity level for the plurality of etching chambers is performed after each of the plurality of etching chambers has been used for a complete duty cycle, and just prior to a scheduled cleaning. Further, the emission intensity level modifier is preferably a graduated neutral density filter.
In an another aspect, the invention provides an etcher having an etching chamber for etching a substrate with an etching process. An emission intensity level detector detects emissions generated while etching the substrate. An emission intensity level modifier modifies the emissions detected by the emission intensity level detector, and substantially maintains a target emission intensity level at an onset of the etching process. An analyzer stops the etching process upon occurrence of a predetermined spectral event sensed by the emission intensity level detector through the emission intensity level modifier.
In yet another aspect, the invention provides an end point detector for detecting an end point of an etching process of a substrate that is conducted in an etching chamber. An emission intensity level detector detects emissions generated while etching the substrate during the etching process. An emission intensity level modifier modifies the emissions detected by the emission intensity level detector, and substantially maintains a target emission intensity level at an onset of the etching process. An analyzer stops the etching process upon occurrence of a predetermined spectral event sensed by the emission intensity level detector through the emission intensity level modifier.